Method of and an apparatus for cutting glass

ABSTRACT

Pieces of flat glass are cut to desired size without the necessity of grinding to size and polishing. Trims are removed from the piece in accordance with a procedure involving the creation of a subsurface discontinuity along an intended path of cut, followed by the application of surface heat along the discontinuity to increase tensile stresses within the piece along the intended path of cut. A bending moment is applied about the intended path of cut to propagate a fracture in the piece of glass. Light seaming of the top and bottom portions of the edges completes the preparation of the edges.

ewes xR 3,800,991

United States Patent 1 1 Grove et al.

METHOD OF AND AN APPARATUS F0 cur'rmc cuss [75] inventors: Robert H.Grove, Sarver; Robert P.

De Torre, Pittsburgh; John R. Dahlberg, Jeannette, all of Pa.

[73] Assignee: PPG Industries, Inc., Pittsburgh, Pa. 221 Filed: Apr. 10,1972 [21] App No; 242,549

[51] Int. Cl. C0311 33/02, 826d 7/10, B26f 3/00 [58] Field of Search225/2, 93.5, 96.5; 65/112, 1 65/1 13 [56] References Cited UNITED STATESPATENTS 2,378,09! 6/1945 McCormick, Jr 225/935 X 3,344,968 10/1967Kovacik et al 225/935 X of the edges.

3, 74,944 10/1969 Chateiain et 14m," 225/935 x v i; PrimaryExaminer-Frank T. Yost 1 I Attorney, Agent, or Firm-Thomas F. Shanahan571 1 ABSTRACT Pieces of flat glass are cut to desired size without thenecessity of grinding to size and polishing. Trims are. removed from thepiece in accordance with a procedure involving the creation of asubsurface discontinuf g ity along an intended path of cut, followed bythe ap A. plication of surface heat along the discontinuity to increasetensile stresses within the piece along the intended path of cut. Abending moment is applied 7 about the intended path of cut to propagatea fracture 1 in the piece of glass. Light seaming of the top and bottomportions of the edges completes the preparation 1s ClaiznsltiDi-awingFigures v "subsurface 1 I METHQB AND AN APPARATUS FOR CUTTING cuss 7BACKGROUND OF THE INVENHQN 1. Field of the Invention: This inventionrelates to a 1 method of and apparatus for producing glass articles,

and in particular, for the manufacture of architectural panels,furniture tops and other relatively thick glass articles, for example,in excess of 10 millimeters (especially in the range of 18 to 36millimeters or above).

2. Description of the Prior Art: in the manufacture ofarchitectural-glass panels and furniture tops of the kind indicatedabove, it has hitherto been common to obtain panels of a desired size byhand scoring and mechanical snapping of the edges of the glass to yielda piece somewhat greater in its dimensions than the final sizedesired,'followed by the grinding of the cut edges of the piece to thedesired size and the polishing of the ground edges. The grinding andpolishing are time-consurning and costly operations, but they havehitherto been considered necessary, particularly in cutting glass sheetsof substantial thickness.

it is important that architectural panels exhibit adequate edgestrength. When tested in accordance with the conventional beam-loadingtest, the ground-andpolished edges of a 4-meter by 8-rneter sheet,approxi mately l8 millimeters thick, produced by a process including thesteps of conventional scoring, snapping, grinding and polishing, exhibitstrength values such as about 4.6 to 49 kilograms per square centimeter.Panels exhibiting values substantially lower than about 4 v flector. Atungsten-filament tubular quartz lamp is uti i cused by theellipticalreflector on the external focal kilograms per squarecentimeter are noticeably more susceptible to breakage.

U.S. application Ser. No. 57,574, tiled July 23, 1970, and U.S.application Ser. No. 68,735, filed Sept. 1, 1970, both by Robert P.De'l'orre, disclose a trimming procedure that involves the applicationof a surface deep score under relatively high pressure by a largediameter, blunt scoring wheel, followed by the propagation of the scoreinto a fracture and a light seaming operation on the top and bottomportions of the edges.

of the glass so cut.

' SUMMARY or THE INVENTION As used in this application, the termssubsurface crack" and subsurface score refer to a discontinuity such asa crack or score, respectively, that is within the thickness of theglass and does not extend to a major surface of the glass. The termsubsurface crack re- The apparatus for performing the abovementloprocess may consist of a subsurface wheel to produce the subsurfacediscontinuity, an infrared line heater to increase the tensile stresseswithin the glass, 2: suitable cut-running apparatus to apply the bendingmoment about the intended path of cut, and a conventional v seamingapparatus.

The subsurface wheel may consist of a large-diameter v scoring wheel,such as, for example, at least approximately 12 millimeters, andpreferably between approximately l9 and lOO millimeters, in diameter,having a blunt cutting angle, such as, for example, betweenapproximately 155 and 170. The wheel is urged against i v a majorsurface of the glass at high forces, such as, for 1 Q example,approximately 80 kilograms to approximately 'f 460 kilograms, and evengreater. A suitable heater is Model 5215 Line Heater, sold by Research,Inc., of Minneapolis, Minnesota. This heater is designed to concentratehigh radiant flux energy on a target line at the external focal axis ofan elliptical reflector. The line is approximately the width of athermal source at the internal focal axis of the elliptical relized asthe source to produce a high temperature (4,000 to 5,400" F.) heat fluxwhich is directed and foment about the intended path of cut and aconventional hand-held belt sander for seaming the upper and bot- 3 ftom portions of the cut edges of the glass. t

It is well known that the easiest cuts to complete are cuts that bisecta piece of glass. Similarly. the most difficult cuts to complete arenarrow trims. This is because of the stresses in the glass at its outerportions. U.S. application Ser. No. 242,5! 1, entitled SUBSUR- FACECRACKS, and filed by Fred Ernsberger and Charles M. l-lollabaugh on aneven date with the instant 40 application, and U.S. application Ser. No.242,510, en-

fers to a. discontinuity substantially without serrations in the glass.The term subsurface score" refers to a discontinuity with serrations inthe glass. The term discontinuity" includes subsurface cracks" andsubsurface scores.

According to the present invention, flat glass is cut along an intendedpath ofcut by producing a disconti- I nuity in the glass along the path,at least a substantial portion of which, along its length, is spacedfrom the major surfaces of the glass. Thermal energy is thenconcentrated on one of the surfaces to create a thermal gradient throughthe thickness of the glass along the intended path of cut to increasetensile stresses in the glass. A bending moment is applied about theintended 6s path of cut to sever the glass. Light seaming removes sharpcomers between the cut edge and each of the major surfaces; Y

titled SUBSURFACE SCORES, tiled by Robert P. De- Torre on an even datewith the instant application, disclose methods of cutting glass usingsubsurface discontinuities. While the cut edges produced by thesemethods are generally of a high quality, trims that are not within thecenter third of the piece of glass often require grinding and polishing.The present invention roduces cut edges of a quality that is equal tothe cut edges produced by the methods disclosed in the abovementionedapplications. However, trims as narrow as 8 to 10 times the thickness of81335 y be removed, I c leaving high quality edges without grindi dpolish it is an object of the present invention to produce cut edgesthat are smooth, strong, staight, pristine and per-. pendicular to themajor surfaces of the piece of glass.

it is a further object of the present invention to pr& 11' V duce suchedges while avoiding the use of grinding and polishing.

It is a further object of the present invention to pro-f I vide a methodand an apparatus for cutting all glass, v and in particular, glassexcess of approximately 10 millimeters in thickness by a relativelyuncomplicated,

procedure. t

It is a further object of the invention to duce cut edges that are atleast equal in quality to those 3 v The remainder of the apparatus maycomprise a conventional cut-running apparatus to apply a bending mo- Ysurface discontinuity;

scoring, with a lesser amount produced by surface deep of seaming.

It is a further object of the present invention to pro-- duce cut edgesthat are at least equal in quality to those produced by subsurfacediscontinuities without an thermal assist, but on narrow trims.

It is a further object of the'present invention to find a practicalmeans for generating a continuous discontinuity that will weaken a sheetof flat glass to the extent necessary s that it may be severed withoutincurring surface crushing or edge damage.

It is a further object of the present invention to pro duce a highquality cut edge at relatively high speeds on relatively narrow trims. I

DESCRIPTION OF THE DRAWINGS A complete understanding of the followinginvention may be obtained from the foregoing and following descriptionthereof, taken together with the appended drawings, in which:

FIG. 1 is a diagrammatic view of a scoring apparatus 2 applying asubsurface discontinuity to a piece of flat glass;

H6. 2 is a vertical cross-sectional view of a cutting wheel used'toproduce subsurface scores;

FIG. 7 is an elevational view ofa cut edge that is produced by a methodusing a sub urface score; and FIG. 8 is an elevation view of a cut edgeof a piece of glass produced in accordance with the present inventionusing a subsurface discontinuity. g

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, anapparatus 12 is shown applying a subsurface discontinuity to a piece ofglass G accordance with the present infor example, to supply thenecessary scoring presure to a cutting wheel by means of a fluidpressure such as air or hydraulic fluid. Further, U.S.'applicaticn Ser.No. l28,384, filed on Mar. 26, 1971, by David A. Bier, sug

gests that a cutting wheel may be actuated by a coni stant-reluctancenrotor means. Any suitable means may to scoring wheel or scorbe used tosupply the load ing wheel 20'.

Referring to FIG. 2, there isshown a detailed view of i i Q I v i v ascoring or cutting wheel 20 made of tungsten carbide or other suitablematerial of hardness of about 7 or more on Mohs' scale and having aradius in excess of approximately 6 millimeters, preferably withinapproximately 9 millimeters to approximately 100 milli- V; J L meters.The base angle, i.e., the angle between the two surfaces 22 and 24, ifextended, is about 120 and the angle between the surfaces 26 and 28(hereafter referred to as the cutting angle) is between approxi- Imately 155 and approximatelyl70", with approxif mately 165 providingoptimumresults. With cutting angles less than approximately l50, defectssuch as l spall and wing may occur. The term spall may be tiej l finedas a chip or flake out of the edge of the piece of glass. The term wing"may be defined as a' lateral FIG. 3 is a vertical cross-sectional viewof a cutting crack on either side of a score line, projected outwardunder the glass surface by the action of a scoring tool. With cuttingangles between approximately 150 and approximately 155, surface deepscores are generally produced. If the cutting angle is greater thanapproximately 170, it is extremely difficult to produce any l. scorebeneath the apex 30 of the wheel 20. if pressure 4 is applied to a wheel20 having a cutting angle greater 7. than approximately 170, until theglass fails, the failure;

will generally occur adjacent to the point where surface 22 meetssurface 26, or surface 24 meetssurface The wheel 20 is shown with acentral axle hole I J which functions as a means for rotatably mountingsaid wheel on a shaft that is passed through the axle hole 32. y

Bolt: 32 may be, for example, 2.4 millimeters in diameter. With such asetup, there is a relatively large amount of friction between thecutting wheel and its holder.

and for this reason, this type of wheel will hereinafter be referred toas a high friction wheel. Wheel 20 may be, for example, 19 millimetersin diameter and urged into contact with a piece of glass G that isapproxialong an intended path of cut and in a direction 14 that issubstantially parallel to top major surface 16 and bottom major surface18, while the glass is supported on a table T. At least a substantialportion of discontinuity 10 is spaced from top surface 16 and bottomsurface 18 along the length of the discontinuity 10. Apparatus 12 isillustrated with a scoring or cutting wheel 20, but a scoring or cuttingwheel 20' may also be used. As the apparatus moves in the direction ofarrow 14, a permanent indentation 11, approximately 0.015 millimeterwide by approximately 0.00l millimeter deep is created above thediscontinuity 10 along the intended path of cut. For the sake ofclarity, the siz of subsurface discontinuity 10 and indentation ll havebeen exaggerated in the drawings.

One skilled in the art will appreciate that it is possible to keepapparatus 12 stationary and move glass G by any suitable conveyor means,such as powered rollers (not shown). There are many commerciallyavailable devices for housing a scoring wheel. his well known,

mately 19 millimeters thick at a force of approximately US kilograms, toproduce a subsurface deep score that starts approximately 0.01millimeter, more or less,

from the top surface 16 of glass G and extends for approximately 2 to2.5 millimeters into the thickness of glass G. Scores so producedcorrespond to the intended location of the edge of the finished piece.To guide the scoring apparatus, a straightedge member may be secured tothe glass G as is conventional in prior-art scor ing.

Referring to FIG. 3, there is shown a wheel 20' that is identical towheel 20 except that wheel 20 has an integral shaft 32' instead of ahole 32. The shaft 32' may be mounted in bearings, such as ball bearings34, to

minimize, or even eliminate, friction between the wheel and a highfriction wheel and these disclosures therefore incorporated herein byreference. l

Although a preferred embodiment of the present invention incorporates acutting wheel or disc, other means will become apparent to carry out thepresent invention. For example, one may wish to construct a member thatcomprises a continuous chain forming a curved cutting edge rather than awheel. It would still be necessary to maintain both the blunt cuttingangles and the high pressures described herein. It is alsov necessary tomaintain the effective radius of the continuous chain within theabove-mentioned range. For example, a continuous chain could take thepath of an oval, but the radius of the oval at the point of contact withthe chain and the glass (effective radius) should be within the samerange as the radius (or effective radius) of a cutting wheel.

It is important to note the importance of orienting the scoring wheelssuch that sides 36 and 38 are substantially perpendicular to the surfaceof the glass to be scored. The subsurface discontinuity generallyextends in the same direction as the cutting wheel. Therefore, if thecutting wheel is not perpendicular to the glass surface, the resultantsubsurface discontinuity will not be perpendicular. Referring to FIGS. 2and 3, angles A and B indicate the angles between the cutting wheel andthe glass surface 16. With a cutting wheel having a cutting angle of165, it is preferred that angle A and angle B be maintained at 7.5".

Referring to FIG. 4, there is shown a diagrammatic view of an infraredLine Heater 40 concentrating thermal energy on the top surface 16 of thepiece of glass G to increase the tensile stresses within the glass. Thedrawing shows a line source 42 of thermal energy that 2 grams per squmemillimeter. if the piece of glass is heated to create a thermal score, astress profile such 6 g V 4 tion. However, in the present invention,tensile stresses I I are created that are of a lesser magnitude thanthose I necessary in thermal scoring.

Referring to Pro. 5, there is shown a diagram illus- I trating threeseparate stress profiles within a piece of glass. An imaginary referenceline R indicates zero stress. Everything to the right of reference lineR indicates tension and everything to the left of reference line Rindicates compression. Curve S, shows the stresses in a piece of floatglass before heat is applied. With such a condition, the surfaces of thepiece arev in compression at about 350 to 425 grams per squaremillimeter, and the center of the piece is in tension at about 210 as S,will result along the intended path of cut. in this case, the surfacecompression and the center tension increase, with the center tensionbeing about 575 preferably has an output of radiation. in the range of a8,500 to l L500 A. wavelength, and necessarily is capable of producingthermal radiations such that the heat applied is great enough to producea stress in tension within the thickness of the glass 6. Line Heaterincludes an elliptically shaped hood 46 that has interiorly thereof, ahighly polished and reflective surface 48. Source 42 is located at theinternal focal axis of elliptically shaped hood 46. As can be seen fromFIG. 4, the elliptical surface 48 is such that radiation emanating fromthe source 42, as indicated by lines 50, 52 and 54, is reflected andfocused at an external focal axis 44. To obtain this result, it isessential that source 42 be located substantially at one of the foci ofthe ellipse that is generated by completing the surface 48, with the ex-1 temal focal axis 44 forming the other focus of said cllipse. U.S.application Ser. No. 66,940, filed Aug. 26, 1970, entitled METHOD OFSEVERING GLASS, by Terrence A. Dear, discloses details of the LineHeater 40 and further elaboration is deemed unnecessary.

it is significant to note that in accordance with the present invention,the glass surface is heated until it reaches a temperature of fromapproximately F. to approximately 130 F. This is substantially less thanthe 200 F. temperature that is necessary for the thermal scoringsuggested in U.S. application Ser. No. 66,940. The present inventionheats the top major sur face 16 of glass G to create a temperaturegradient throughout the piece of glass G. The temperature of top majorsurface 16 may be, for example, F., while the temperature of the bottommajor surface 18 may be, for example, 70 F. This temperature gradientcreates a stress profile in the glass that is similar to the stressprofile that one obtains in the thermal scoring process taught in theabove-mentioned Dear applicagrams per square millimeter. This result isachieved whenthe temp rature of the top major surface of the glass isappriiximately 200 F. In accordance with the present invention, a stressprofile such asS will result along the intended path of cut. Here thetop surface of the glass is heated to approximately R00 to P. so

that the center tension is increased only to approximately 425 grams persquare millimeter to aid a subsurr face discontinuity in guiding afracture.

The present invention may be distinguished from the thermal scoringtechniques suggested in U.S. application Ser. No. 66,940, in that thepresent invention does- I not create tensile stresses as high as thosecreated with 1 I thermal scoring, since the present invention utilizes asubsurface discontinuity, and not a buildup of stresses,

to guide a fracture. This is very significant when one considersnon-bisecting cuts or trims. With the thermal scoring techniques taughtin U.S. application Ser. No.-

66,940, banana edges are obtained in non-bisecting cuts, but with thecut 'ng techniques of the present invention, banana edges" are avoidedbecause the sub- 40 surface discontinuity guides the fracture.

With the cutting techniques involving subsurface dis-- continuities, astaught by either Ernsberger and Hol-. 1 labaugh, or DeTorre, grindingand polishing is usually I necessary on attempts to cut a piece of glassalong a path that is not within the center one-third of the piece.-

The present invention is an improvement over these techniques in that itassists the subsurface discontinuityby applying heat along thediscontinuity to create tensile stresses within the glass that helpprovide high qual-v :7 i ity edges, even ontrimcuts. v

In accordance with the present invention, it is possii ble to create thenecessary tensile stresses in the piece of glass either by holding theheater fixed or stationary with respect to the glass or by providingrelative movemerit between the heater and the glass. For example, if

a 6l-centimeter Line Heater is fixed with respect to a piece of glass,and it radiates 39.4 watts per lineal centimeter to an external focus 44which corresponds to an intended path of cut that is 25.4 centimetersfrom one I side of the piece of glass that is 61 centimeters by 61.centimeters, the approximate times to create the necessary tensilestresses are as follows: for glass 25.4 millimeters thick, l0 seconds;for glass 19 millimeters thick, 8 seconds; for glass 13 millimetersthick, 6 seconds; for

glass 8.5 millimeters thick, 4 seconds; for glass 6.5 milv limetersthick, 3 seconds; and for glass 3 millimeters" 1 f thick, 2 seconds, Ifthe power increases to 78.8 watts r 7 per lineal centimeter, the timesdecrease to: 7 seconds for 25.4-millimeter thick glass; seconds for 19-millimeter thick glass; 3 seconds for l3-miilimeter. thick glass; 2seconds for 8.5-miilimeter thick glass; 1.5

seconds for 6.5-millimeter thick glass; and 1 second for 3-millimeterthick glass. At higher levels of flux density (power per unit of energyconcentrated at the external focus), less time is required.

. When the tensile stresses are created while there is 7 relativemovement between the heater and the glass, such as either the heater orthe glass (or both, where each moves at a different speed) moving intoor out of the paper in FIG. 4, there-is a certain maximum speed oftraverse at which the Line Heater 49 or the glass G may be moved. Usinga Line Heater that is centimewheel. The top surface of the glass isthere designated with the numeral 16 and the bottom surface designatedwith the numeral 18. A short distance below top sur face to is seen amarking 80 and a marking 82 which.

indicate the extent of the subsurface score. The marking 88 is generallyapproximately 0.01 millimeter, more 82 eachapproximate a straight linethat is parallel to top surface 16 and bottom surface 18. I

ters long at a rated power of 1,200 watts to create the tensile stressesin a piece of fil-centimeter glass along a path that is 25.4 centimetersfrom one side of,the

piece, maximum scan speeds are approximately: 46 centimeters per minutefor glass 25.4 millimeters thick; 64 centimeters per minute for glass 19millimeters thick; 98 centimeters per minute for glass l2.7 millimetersthick; and i3? centimeters per minute for glass 6.35 millimeters thick.Y

it should be understood that while the invention has thus far beendescribed as including a Line Heater to alter the stress profile in apiece of glass, it is not limited to such. Any thermal source that iscapable of concentrating thermal energy along a narrow path that is notmore than approximately 6.4 millimeters in width to create a tensilestress of approximately 425 grams per square millimeter within the glasswill be suitable. For example, spot heaters (such as the one disclosedin the V above-mentioned Dear application), hot air heaters (such as thein-line array disclosed in US. application Ser. No. 72,354), and lasers,are capable of creating such stresses without damaging the surfaces ofthe glass or the cut edge.

Referring to FIG. 6, there is shown an elevation view of a snappingapparatus 70 in position to apply a bending moment about subsurfacediscontinuity 10. The apparatus may consist of two top anvils 72 and 74,and a bottom anvil 76. Glass G may be placed upon a table so that aportion of the subsurface discontinuity l0 overlaps the table. A bendingmoment may be applied at the end of the piece of glass G that overlapsthe table to run a out along the subsurface discontinuity l0. lt issometimes difficult, especially with pieces of glass that are relativelylong and thick (such as l9-millimeter thick glass in excess of 3 metersin length), to run a cut in the manner described. Under suchcircumstances, a narrow member or plate, approximately l2 millimeters inwidth, may be placed between the glass and the table, directly beneaththe subsurface discontinuity 10. This places the top surface of thepiece of glass in tension along the discontinuity and reduces the energynecessary to run a cut along the entire length of the piece. Cut edgesare produced that are smooth, strong, straight, pristine andperpendicular to the major surfaces of the piece.

After the glass has been snapped, there may be conducted an inspectionto determine the quality of the cut edge that has been opened. In theinspection along the cut edge, looking perpendicularly to the cut edge,it is customary to see a pattern such as that indicated in FIGS. 7 and8. FIG. 7 illustrates a cut edge that was severed with a subsurfacescore, using a high friction Referring to P26. 8, there is shown a cutedge at a piece of glass G that was severed with a subsurface crack,using a low friction wheel, such as wheel 20'. I (3 The edge in FIG. 8is similar to the one shown in H6.

7, except for a smooth area 84' between marking 80 and marking 82'. Area84' is substantially free of serrations because the circular defectsthat cause serrations are eliminated with subsurface cracks- Theinspection further comprises viewingjthe glass vertically, i.e.,inadirection perpendicular to the major surfaces of the sheet of glass,to detect wing or undercut defects. A satisfactory cut exhibits no suchdefects, or, at the worst, ones so minor as to be removed during asubsequent seaming operation.

As a final step in the process of the present invention, there isconducted a finishing, such as light seaming, of the upper and bottomportions of the edges of the piece of glass so cut. This leaves a smoothedge with no evi- I dence of markings or serrations. There may be used,for example, a hand-held belt sander using a belt'600 millimeters longby 75 millimeters wide. this is a conventional operation, and it doesnot require further elaboration nor explanation. p

The result is that there is produced a finished piece of glass thatcompares favorably in its edge strength to similar pieces produced bythe prior-art method of rough cutting, mechanical snapping, grinding tosize, and then polishing. Pieces of the present invention have edgestrengths of approximately 4.4 to approximately 4.7 kilograms per squarecentimeter in the conventional beam-loading test, in comparison withstrengths such as 4.6 to 4.9 kilograms per square centimeter for theprior-art ground-and-pclished pieces. Either will meet specifications oncustomary glazing installations. in achieving the edge-strength valuesindicated above,

the final limited seaming operation is important. Without the finalseaming operation, the edge strength is on m the order of 3.8 to 4.0kilograms per square centimeter; v v I Referring to Table A, there isshown the ranges of force that may be applied to cutting wheels of varlens diameters, and the depths of subsurface discontinuities thatresult. The table also indicates the approxi-- mate maximum speeds withwhich a high friction wheel and a low friction wheel may be advanced toinsure that, V

TABLE .5. i

' Maximum Maximum speed for speed for Y e produdng producing dep h ofsubsurface subsurface Wheel Range subsurface score (cancrack diameter,of force, discontinuity, timeters/ t mllLm eters second) second) 1.54.525 l. 7-2.7 30 1. 2. 0-3. 0 40 1. m0---.-. wit-460 2.5-4.0 so a V glassis a subsurfacescore.

It is anticipated that the present invention may be used to cut edgesother than straight edges. Further, bent or other forms of flat glassmay also be cut as Having now fully disclosed the invention, what weclaim is as follows: 1

l. A method of cutting flat glass along an intended path of cutcomprising the steps of:

producing a discontinuity in said glass extending substantiallyperpendicular to and along said path, at least a substantial portion ofwhich, along its length. is spaced from the major surfaces of saidglass. 7 concentrating thermal energy on one of said surfaces to createa heat gradient through the thickness of the glass along said intendedpath of cut to increase tensile stresses in the glass, and applying abending moment about said intended path of cut to sever said glass. V 2.A method of cutting flat glass as defined in claim I, wherein thediscontinuity that is produced in said 3. A method of cutting flat glassas defined in claim 1, wherein the discontinuity that is produced insaid glass is a subsurface craclt. I

4. A method of cutting flat glass as defined in claim I, wherein thediscontinuity is produced by a wheel having a cutting angle of fromapproximately 155 to approximately 170 and a diameter of atlastapproximately 12 millimeters.

5. A method of cutting flat glass as defined in claim 4, wherein saidwheel is forced against said one of said surfaces at a force betweenapproximately 40 and approximately 460 kilograms.

6. A method of cutting flat glass as defined in claim 4, wherein saidwheel is forced against one of said surfaces at a force aboveapproximately 8 kilograms.

7. A method of cutting flat glass as defined in claim 4, wherein saidwheel is forced against said one of said surfaces at a force aboveapproximately 80 kilograms.

8. A method of cutting flat glass as defined in claim 1, wherein thestep of concentrating thermal energy comprises activating a thermalsource and focusing radiant energy from said thermal source on said oneof said surfaces by an elliptical reflector.

9. A method of cutting flat glass as defined in claim 1, wherein thestep of concentrating thermal energy comprises activating an in-linearray of hot gas heaters. y, or

10. A method of cutting flat glass as defined in claim 8, wherein thereis no movement between the heater and the glass when the thermal energyis concentrated on one of said surfaces. a

11. A method of cutting flat glass as defined in claim 8,. wherein thereis relative movement between the heater and the glass when the thermalenergy is concentrated on said one of said surfaces.

12. A method of cutting flat glass as defined in claim 9, wherein thereis no movement between the heater and the glass when the thermal energyis concentrated on one of said surfaces.

13. A method of cutting flat glass as defined in claim 9, wherein thereis relative movement between the heater and the glass when the thermalenergy is concentrated on said one of said surfaces.

14. A method of cutting flat glass as defined in claim 8, wherein heatis concentrated on said one of said surfaces until said one ot saidsurfaces is between approximately 105 F. and approximately 125 F.

15. A method of cutting flat glass as defined in claim 9, wherein heatis concentrated on said one of said surfaces until said one of saidsurfaces is between approximately 105 and approximately 125 I UNITEDSTATES PATEE-yr FFzcE I H, v J:

Patent No. 3,800,991 meg April 2, 1974 Inventofls) Robert H. Grove et 31It is certified that errcr appears in the aboveidentified patent andthat said Letters Patent are hereby corrected as shown below:v

Column 9, line 42, C1aim 5, change "between" to at l eas t-m Column 9,lines 42 arid 43, Claim 5, de1ete "a nd approxiihately 460".

Column 10, lines 4 through 6, Claim 7, delete n. its ntirety} 1 thecover sheet, after the a bstraem li Cleinie".should*e i ji read 5- 14Claims Signed and sealed this 24th day'of ,Se p temb er (SEAL) Attest; Iv I I MCCOY M. GIBSON v .v I v HALL 4D I V I Attesting Officerj Y Hccnmissioner of Patent uscorm oc oos're-Pu f I UNITED STATES PATEE-yrFFzcE I H, v J:

Patent No. 3,800,991 meg April 2, 1974 Inventofls) Robert H. Grove et 31It is certified that errcr appears in the aboveidentified patent andthat said Letters Patent are hereby corrected as shown below:v

Column 9, line 42, C1aim 5, change "between" to at l eas t-m Column 9,lines 42 arid 43, Claim 5, de1ete "a nd approxiihately 460".

Column 10, lines 4 through 6, Claim 7, delete n. its ntirety} 1 thecover sheet, after the a bstraem li Cleinie".should*e i ji read 5- 14Claims Signed and sealed this 24th day'of ,Se p temb er (SEAL) Attest; Iv I I MCCOY M. GIBSON v .v I v HALL 4D I V I Attesting Officerj Y Hccnmissioner of Patent uscorm oc oos're-Pu f UNITED ST/ITES PATENTOFFICE CERTIFICATE OF CORRECTION Patent No.- 3,800,991 Dated April 2,1974 Inventor(s) Robert H. Grove et l It is certified that error appearsin the above-identified patent and that said Letters Patent are herebycorrected as shown below:

Column 9, line 42, Claim 5, change "between" to --of at least--.

Column 9, lines 42 and 43, Claim 5, delete "and approximately 460".

Column 10, lines 4 through 6, Claim 7, delete in its entirety.

On the cover sheet, after the abstract, "15 Claims" should read 14Claims Signed and sealed this 24th day of September 1974,

(SEAL) Attest:

MCCOY M. GIBSON JR. I I C. MARSHALL DANN Attesting Officer Conmissionerof Patents :ORM PC4050 (069) USCOMM-DC 60376-P69 U. S. GOVIINMINT'RHTING OFFlCE i I". 035 l.v

1. A method of cutting flat glass along an intended path of cutcomprising the steps of: producing a discontinuity in said glassextending substantially perpendicular to and along said path, at least asubstantial portion of which, along its length, is spaced from the majorsurfaces of said glass, concentrating thermal energy on one of saidsurfaces to create a heat gradient through the thickness of the glassalong said intended path of cut to increase tensile stresses in theglass, and applying a bending moment about said intended path of cut tosever said glass.
 2. A method of cutting flat glass as defined in claim1, wherein the discontinuity that is produced in said glass is asubsurface score.
 3. A method of cutting flat glass as defined in claim1, wherein the discontinuity that is produced in said glass is asubsurface crack.
 4. A method of cutting flat glass as defined in claim1, wherein the discontinuity is produced by a wheel having a cuttingangle of from approximately 155* to approximately 170* and a diameter offrom approximately 12 millimeters to approximately 100 millimeters.
 5. Amethod of cutting flat glass as defined in claim 4, wherein said wheelis forced against said one of said surfaces at a force betweenapproximately 40 and approximately 460 kilograms.
 6. A method of cuttingflat glass as defined in claim 4, wherein said wheel is forced againstone of said surfaces at a force above approximately 80 kilograms.
 7. Amethod of cutting flat glass as defined in claim 4, wherein said wheelis forced against said one of said surfaces at a forCe aboveapproximately 80 kilograms.
 8. A method of cutting flat glass as definedin claim 1, wherein the step of concentrating thermal energy comprisesactivating a thermal source and focusing radiant energy from saidthermal source on said one of said surfaces by an elliptical reflector.9. A method of cutting flat glass as defined in claim 1, wherein thestep of concentrating thermal energy comprises activating an in-linearray of hot gas heaters.
 10. A method of cutting flat glass as definedin claim 8, wherein there is no movement between the heater and theglass when the thermal energy is concentrated on one of said surfaces.11. A method of cutting flat glass as defined in claim 8, wherein thereis relative movement between the heater and the glass when the thermalenergy is concentrated on said one of said surfaces.
 12. A method ofcutting flat glass as defined in claim 9, wherein there is no movementbetween the heater and the glass when the thermal energy is concentratedon one of said surfaces.
 13. A method of cutting flat glass as definedin claim 9, wherein there is relative movement between the heater andthe glass when the thermal energy is concentrated on said one of saidsurfaces.
 14. A method of cutting flat glass as defined in claim 8,wherein heat is concentrated on said one of said surfaces until said oneof said surfaces is between approximately 105* F. and approximately 125*F.
 15. A method of cutting flat glass as defined in claim 9, whereinheat is concentrated on said one of said surfaces until said one of saidsurfaces is between approximately 105* F. and approximately 125* F.